As I understand it, the field coils and armature windings in a DC motor are insulated and this insulation can 'burn off' if the motor overheats, causing a short circuit to develop. What is the material coating the windings and coils in a DC motor? In the examples of the insides of DC motors that I have seen, the windings still retained the look of copper wire - does this mean that the coating is transparent? If so, is this always the case or are there winding coatings that are not transparent?
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\$\begingroup\$ The only opaque coatings I have seen on copper or aluminium 'magnet wire' have been wound silk or mica impregnated coatings on old or heavy service applications respectively. Translucent is the norm but there is no reason a compatible pigment or dye could not be investigated if a customer was demanding enough. \$\endgroup\$– KalleMPCommented Jan 2, 2019 at 19:30
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Wire used for motor windings, transformers and other electro-magnetic applications is called magnet wire. Magnet wire insulation is similar to polyurethane varnish. However is is developed specifically for electrical insulation use. As you have observed, the insulation is quite thin yet able to withstand the normal operating temperature and voltage required for motor windings. It is not completely transparent. It is sometimes colored green or other colors that do not look like copper. The most common color is similar to copper. There doesn't seem to be any particular reason to use other colors.
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\$\begingroup\$ The colours are mostly used to differentiate the ends of various pole windings in a motor or taps in a transformer. Different vendors may use then to differentiate according to specification. Some may even offer then in colours for ornamental purposes. Modern earbud wires have loose wire bundles that are colour coded for L, R and GND \$\endgroup\$– KalleMPCommented Nov 6, 2018 at 12:28
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Various polymers are used depending on the temperature required. Look up 'Magnet wire' on Wikipedia. I haven't seen opaque 'enamel' used.
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\$\begingroup\$ Some magnet wires have an over coating that can be softened with heat or solvents to glue the wires into a solid pack. \$\endgroup\$– KalleMPCommented Nov 6, 2018 at 12:29
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\$\begingroup\$ Thank you @KalleMP, I didn't know that. Can you give an example? \$\endgroup\$ Commented Nov 7, 2018 at 5:35
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\$\begingroup\$ Google search for self-bonding magnet wire. Lots of examples and vendors. Also on Youtube. \$\endgroup\$– KalleMPCommented Nov 7, 2018 at 8:30